That power supply only produces 12v and just a tiny bit of 5v, probably barely enough to be classified as 5v standby, so you should ignore it.
You can't make it produce 5v or 3.3v like a computer needs because it's missing the electronics inside to do it. You would need to add the 3.3v and 5v dc-dc converters and then put the wires in the atx connector and the molex connectors and so on.
It's probably a job that's too difficult for you, because computers still require about 6-10 amps on 5v and about 5 amps on 3.3v and you can't achieve these with cheap ebay dc-dc converters.